1. Field of the Invention
The present invention relates to an automatic focusing apparatus which can be applied to an auto-level or a transit instrument etc., having a telephotographic system.
2. Description of the Related Art
A surveying instrument having a telephotographic system is basically provided with a collimating telescope.
In general, a surveying instrument is provided with a focusing apparatus which enables an operator to view a clear object image regardless of the distance of the object being viewed (aiming object). That is, it is necessary for an operator to actuate the focusing apparatus, while observing the aiming object through the collimating telescope, to view the object in a clear state. Consequently, a conventional auto-level suffers from the defects that the operator cannot concentrate upon the collimation operation due to the focusing operation, and that it takes a long time to complete the focusing operation. Due to these circumstances, an automatic focusing apparatus has been needed. However, if focusing cannot be carried out using the automatic focusing apparatus, or if the operator wants to manually control the focus, a manual focusing operation is further required.
In particular, in a surveying instrument which is often used outdoors, a dry battery (primary battery) or a rechargeable battery (secondary battery), etc., having a limited capacity is used as a power source for the automatic focusing apparatus. Consequently, the operation time of the automatic focusing apparatus is limited due to the limited capacity of the battery. There is a need to increase the operation time.